Process for blackening copper and copper alloys



Patented July 12, 1949 PROCESS FOR BLACKENING COPPER AND COPPER ALLOYSIsaac Laird Newell, Wethersfield, Conn., assignor to HeatbathCorporation, Indian Orchard,

Mass, a corporation of Massachusetts No Drawing. Application'August 1,1946, Serial No. 687,697

9 Claims.

This invention relates to-a process for blackening copper and copperalloys and has for its object the attainment of highly successfulresults in producing a black coating on such metal parts without thedisadvantagesattendant upon the use of baths heretofore used'for thispurpose.

Up to the present time, the art of blackening copper and copperalloys-has been confined for the most part to processes which give anoxide or sulphide film on the surface. While the baths to produce theblack sulphide films are comparatively simple and easy to operate,non-toxic and free from explosion and fire hazard, the film is, however,rather soft, and its adhesion to the metal surface is poor. Moreover,the sulphide film can only be produced satisfactorily on copper oralloys very high in copper. Other copper alloys would need to be copperplated before blackening. A protective coating of lacquer or wax isnecessary to preserve the sulphide film and insure its permanence.

Black copper oxide films have been producedon copper and copper alloysby a number of methods. This black oxide is a durable coating andadheres tenaciously to the base metal. The black oxide film, moreover,can be produced in either a dull or shiny finish. However, the bathsformerly used to produce the black copper oxide coatings have had manydisadvantages. One commonly used bath compound of copper carbonate andammonium hydroxide is diificult to operate because of the sensitivity ofthe bath to deficiencies or excesses of ammonium hydroxide. The bathalso has a short life and must be discarded when used for only a shorttime.

Another type ofbath composed of caustic soda and sodium chloriteproduces a satisfactory black copper oxide coating, but has thedisadvantage of being composed partly of a hazardous sub stancesodiumchlorite. This material is especially hazardous in the dry state as itis a powerful oxidizing agent. Wood, cloth, paper and other commonpackaging materials are rendered highly inflammable by the sodiumhydroxide-sodium chlorite mixture.

I have discovered that a bath comprising a water solution of a Watersoluble salt of an aryl sulphone monochloramide made alkaline with astrong water soluble alkali is free of the objections above mentionedand is effective for use suitable for use in a copper blackening bath.One compound of this group particularly suitable from the standpoint ofcommercial use, is the sodium salt of benzenesulphonemonochloramide.This organic compound is not hazardous from the standpoint of fires andexplosion in either the dry state or in solution. Baths forblackeningcopper employing this material can vary widely in proportion,yet give a suitable black. As little as by weight of the sulphonemonochloramide and A; of water soluble alkali give excellent blackeningbaths. Large amounts also produce satisfactory baths and the amounts arelimited by the solubilities of the components. However, there is noadvantage in the use of higher concentrations and because of economicreasons I prefer the more dilute solutions.

Among the strong water soluble alkalies acceptable for this compositionare those of the alkali metal and alkaline earth metal groups. While thecarbonates of some of these are satisfactory, the alkali metalhydroxides appear to be most suitable.

Of the copper alloys tested with this bath, I have found thosecontaining zinc, lead, tin, phosphorus, silver, aluminum, silicon andberyllium to give unusually good black coatings. 'I do not limit myself,however, to the alloys mentioned above, and this list is given to showthe wide range of alloys which may be blackened by my process.-

'Herewith are given by way of example several specific disclosures of myprocess for the black coating of copper and two of its principal alloys.

Example N0. 1.--For copper Two parts by weight of the sodium salt ofbenzenesulphonemonochloramide and two parts by weight of sodiumhydroxide are dissolved in parts by weight of water. This solution isheated to a temperature of F. and the piece of copper to be coatedpreviously cleaned by the customary mechanical and chemical methods isimmersed in the bath for a period of from 5 to 15 minutes. Upon removingthe copper piece from the bath, it is rinsed in water for a sulficientlength of time to remove completely any residue from the alkaline bathand is then dried. A durable, velvety, jet black coating which adherestenaciously to the copper piece will be present on its surface. Thiscoating can be made shiny by logues as part of the molecule, to beespecially 55 gentlebuffing orby means of oil or wax finishes.

3 Example No. 2.--For brass (85% copper, 15% zinc) Two parts by weightof the sodium salt of toluenesulphonemonochloramide and two parts byweight of potassium hydroxide are dissolved in 100 partss-by weight ofwater. "This solution is heatedto boiling, and the piece'of brass to becoated, previously cleaned by the customary mechanical and chemicalmethods is immersed in the bath for a period of from,.5-.to :15 minutes.Upon removing the brass piece from the-bath, it is rinsed in water vfora sufficient length of time to remove completely any residue' frcvmthealka line bath and is then dried. "A- durablefvelvety, jet blackcoating which adheres tenaciouslyto the brass piece will be presentLohits :surface. This coating can be made shiny by gentle bufling or bymeans of oil or wax finishes.

Example No. 3.For beryllium copper "i'Iwo j'pa'rts by weight of thesodium salt :of benzene tsulphone monochloramide "and four partsi byweight of sodium carbonate are dissolve'd'iin 100partszby weightoflwater; This solution ris heated to a temperature "of 200 F.andia-pi'ece of beryllium copper to be coated, previously'eleaned byithecustomary mechanical and chemical methods is a immersed in 'the bath foraipverio'd of fromf5ito'15 minutes. Upon-removingithe piecefifrom-the'bath, itiis rinsed in water for-a sufficient length *oftime to removeoompletely any residuetfrom the alkaline bath and is thendried. 1Adurable,velvety, jet blacktcoating whichadheres 'tenaciously to thepiece will' be presentron' its surface. .This coating canbema'de'shinyibyfgentle.buffing or by imeans 'of-ioil or waxfinishes.

It is to be understood that the organic-ashlphone :monochlorami'desgiven in' the above examples areinot'confinedto the examples cite d butmay be interchanged. Moreover, other organic sulphone'monochloramides'of this *type may b'ersubstituted. In. likemanner thealkalies used may be interchanged.

The "temperature of the bath forthe blackening 'operationrzis'notlimited to those :giverrin" the examples. The temperature may-varywidely and theirate' of blackening w'ill be relativelylow at lthellowerltemperatures and high at the' higherttemperatures. I have 'found that:temperatures aslow as 1.125? .F.'wi1l produce .a satisfactory black,but is time consuming. Temperatures 'ibetween 1175 "and boiling zwill:be iiound to "be mvstasuitabl'e for blackening baths.

1. The process of blackening copper and its alloys in which the metalisimmersed in a solution consisting of 2 parts of the sodium salt .ofbenzene sulphone "monochloramide, 2 parts of sodium hydroxide and100'parts otwat'er', said solution being. heatedto a temperature between175 Rand boiling, and the metal iheldin'said solutionfor'a sufficienttime toproduce'the des'ireddepth of color.

'2 Thepro'cess Iof blackening copper and its allbys in whichthemetal isimmersed in asolution consisting-of 'a water solution of a'watersolublesalt of an aryl sulphone monochloramide made'alkaline-with astrong water solublefixed alkali, said 'solution bein'gheate'd to atemperature i between 175 -'F. and T boiling and l the metal heldiinisaid-solution for a sufiici'ent time to -producezthe desired zdepth'pfiblack.

:siul'he pro'cesslof 'claim z izriwhicmtm propor 4 tion of aryl sulphonemonochloramide to the strong water soluble fixed alkali is 1:1.

4. The process of blackening copper and its alloys in which the metal isimmersed in a solution consisting of a water solution of a water soluble.salt of an aryl sulphone-monochloramide made alkaline with a strongwatersoluble fixed alkali in which the organic group of the sulphonechloramide compound consists of a homologue of benzene, said solutionbeing heated to a tem- :perature between'1'75" F. and boiling and themetal held in said solution for a sufficient time :to produce.thedesired depth of black.

fiiTheexprocess .of blackening copper and its alloysiinwhichithe.metalis immersed in a solution consisting of .a water solution of the sodium.salt of benzene'sulphone monochloramide made alkaline with a strongwater soluble fixed alkali,

, saidrsolution being heated to a temperature between 175 F. and boilingand the metal held in SaidfSOIUtiOII'fOI a sufiicient time to producethe desired depth :of black,

-;6. The process of blackening copper and its alloys sin whichthelmetal. is immersed in a .solution consisting of a water solution ofthesodium salt of toluenesulphonemonochloramide made alkalinewithastrong water soluble .fixed alkali, said-" solution .beinghea-ted.to a temperature-between 1-75" F. and vboiling and the metal-heldinsaid solutionrior a sufficient time .to producelthe desired depth ofblack. v

-7. The process of blackening copper and its alloys'in whichthe metal isimmersed in a solution consisting of a water-soluti0n of a watersolublesalt of an aryl sulphonemonochloramide made alkalinewith analkali metal hydroxide, said solution beingiheated vto a temperaturebetween 175 F. an'd'boiling and themetal heldvin said solution for asufficient time to produce the desired depth of .black'.

8. The process of claim 6..in whichtheproportion of organicsulphonevmonochloramide to alkali .met'al hydroxide is 1.2.1 and the rsolution strength l is 4 parts by weight .of: said. compounds to:100parts by weight of water.

9..-' 1he,,process of blackening copper andits alloys intwhich the metalislimmersed in asolution consisting of a water solutionof a watersoluble-salt of-an-aryl sulphone monochloramide made alkaline with an'alkali metal carbonate,

.said solution being-heated to 1 a temperature between .1.'l5- F. and.boiling and the metal held in said solution .for .asuflicient time. toproduce the-desired depth of black.

ISAAC LAIRD NEWELL.

' REFERENCES CITED The :Iollowing :reierenlces are: of record in vthefile of this patent:

UNITED" STATES PATENTS Number I Name. Date 1,650,124 Gunzler et -.al.Nov. 22,.1927 1,769,852 vOgden July 1, 1930 1,890,603 Feibelmann in"...Deep 13, 1932 -1,892,548 Feibelmann 1-.-- Dec. -27, 1932 .1.,a9'4;5e9.-Mirau4-. a Jan, .17, 1933 "23641993 Meyer .Dec. .12, 1944:EOREIGNTPATENTS Number Country v Date.

4239164 '=Germany 'May 12, 1926 5903376; *-France' Marf27, 1925 $47566 T"Germany 1 July 711937

